Adding test for required fields

ktoml-core/src/commonTest/kotlin/com/akuleshov7/ktoml/decoders/RequiredAnnotation.kt

@@ -0,0 +1,24 @@
+package com.akuleshov7.ktoml.decoders
+
+import com.akuleshov7.ktoml.Toml
+import com.akuleshov7.ktoml.exceptions.MissingRequiredPropertyException
+import kotlinx.serialization.Required
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.decodeFromString
+import kotlin.test.Test
+import kotlin.test.assertFailsWith
+
+@Serializable
+data class RequiredStr (
+    val a: String =  "a",
+    @Required
+    val b: String = "b",
+    val c: String,
+)
+
+class RequiredAnnotation {
+    @Test
+    fun testMissingRequiredPropertyException() {
+        assertFailsWith<MissingRequiredPropertyException> {  Toml.decodeFromString<RequiredStr>("c = \"100\"") }
+    }
+}